Ozone is an excellent oxidizing agent and is highly destructive to many microorganisms, such as bacteria, fungi and algae. Thus, ozone has found uses in water purification, sterilization and deodorization. In many applications, ozone is more effective than chlorine, while the oxidation product of ozone is typically a harmless and environmentally acceptable gas, such as carbon-dioxide or water. However, the high cost and lack of long-term reliable ozone producing equipment has retarded the widespread use of ozone in many commercial applications.
Apparatus generating ozone are sometimes called "ozonators". In a typical corona discharge ozonator, the electrodes are made of aluminum, copper, steel or stainless steel. The dielectric is usually glass, titanium dioxide or alumina, and is either attached to one of the electrodes or positions in close proximity to it.
U.S. Pat. No. 4,417,966, issued Nov. 29, 1983, inventors Krauss, et al discloses a typical corona discharge ozonator where conventional cooling by means of air or water is suggested. The known, or conventional, cooling of such a corona discharge ozonator is to water-cool one of the two electrodes. The other electrode is usually difficult to cool because it is on high electric potential, but some cooling is achieved by convection using the air being ozonated in the gap, and by radiation through the gap. Both are very inefficient cooling mechanisms, especially in view of the fact that ozone is known to recombine to diatomic oxygen at a quickly increasing rate with increasing temperature.
U.S. Pat. No. 4,213,838, issued July 22, 1980, inventor Lowther, describes a corona discharge ozonator where the heat generated by corona discharge is said to be removed by the gas flow itself in a high rate of gas flow. This gas flow is conducted at a rate such that the pressure drop over the gas flow path is maintained between 0.1 and 2.0 pounds/inch.sup.2, the flow path is between 2 and 10 inches in length, and a gap is between 0.01 and 0.25 inch.
European Patent Application publication number 160,964, published Nov. 13, 1985, inventor Masuda, discloses a corona discharge ozonator in which the gas being flowed is pressurized and cooled to make the density of the gas higher than that in the standard state. A cooling device comprises cooling fins on the outer periphery of the feed pipe, as well as on the outer peripheral surface of the cylindrical dielectric.
U.S. Pat. No. 4,774,061, issued Sept. 27, 1988, inventor Ahlbrandt, discloses an open station corona treating system for treating the surface of sheet materials by electric brush discharge. A brush electrode is cooled by air during the treatment process.
However, temperatures of any component in the airstream being flowed through the ozonator above about 120.degree.-150.degree. F. (about 49.degree.-66.degree. C.) are prohibitive, and at such relatively low temperatures and temperature differentials the conventional convection and radiation cooling is not very effective. The discharge energy intensities that can be drawn are thus limited, and the ozonators become bulky and expensive. Accordingly, there is a need for corona discharge ozonators with better cooling for improved ozone output to reduce the cost per unit ozone production.